The key technique in difficult process control is to make the control loop faster than the process.   This requires final element positioning of high dynamic response.   Hydraulic-electronic positioners have the basic high stiffness and precise and rapid reversal capabilities which produce infinite resolution of valve position with high frequency response.   As a rule, the better these characteristics, the faster and more precise the return to control after an upset.

Particularly in refinery valves, very high torques are needed to insure freedom from valve sticking.   Hydraulic drives are required to obtain these torques.



  1. Hydraulics are readily modulated or controlled in both force and velocity
  2. Hydraulics have very high efficiencies in conversion of pressure to thrust
  3. Hydraulics provide convenient energy storage that can be used for high speed modulation or shutdown operations.   
  4. Hydraulics operate over a wide range of velocities and pressures.
  5. Maintenance costs of hydraulics are lower as all moving parts
    are submerged in hydraulic fluid and continually lubricated.
  6. Noise levels are dramatically reduced - no air venting to atmosphere.
  7. No concern for wet air supply freezing in cold weather.
  8. Size to force output ratio is much greater than with pneumatics - hydraulic actuators are 75% smaller than pneumatic actuators.
  9. Eliminate leakage with leak proof components and connections using manifold construction and SAE Code 61 pipe and tube fittings.
  10. LVDT internally mounted to protect from atmosphere.
  11. No external moving pressure seals
  12. By using jet pipe servovalves, systems are much more dirt tolerable than existing servo controlled hydraulic systems